Electrical cut-out



April 23, 1935. w. J, 'DAW ELECTRICAL CUT-OU'I1 Filed Aug. 15, 1931 4. 2. f 2 8 I C FW /.|,J. 2 ,/7/ mo 2 2 6 7 9 9 @f l //Mff A, fo w WWW/WWW, 4%, 2

Ill

V sulating material.

Patented Apr. 23, 1935 UNITED STATES 1,999,124' ELECTRICAL CUT-OUT William J ames Davy,

East Croydon, England Application August 15, 1931, Serial No. 557,420

In Great Britain 10 Claims.

, This invention relates to electrical cut-outs wherein the ordinary fusible element is replaced by a column of mercury of relatively small crosssectional area contained in a tubular body of inl When the column of mercury is subjected to an abnormal flow of electric current the column is ruptured, probably by vaporization due to thermal action, and a portion o the mercury is expelled from the tube so breaking the electricalY circuit through the column.

The object of'this inventionis to provide improved and simplified constructions of such cutouts which shall be eiiicient and reliable in operation and which shall comprise simple and effective means for .re-establishing continuity in the mercury column.

f An electrical cut-out according to the present invention comprises an insulating tube, preferably of some refractory material, metallic pieces at both ends of the tube to make Contact betweenv the ends of a mercury column contained within the tube and the external electrical circuit to be controlled by the cut-out, an expansion chamber to contain any mercuryV expelled from the tube upon rupture of the mercury column therein and means for returning such expelled mercury back f into the tube for re-establishing electrical continuity through the mercury column.

In the accompanying drawing; Figs. l to 6 are longitudinal sectional views of various forms of cut-outs constructed in accordance with `this invention; Fig. 7 is a transverse section oi that cutout shown, in Fig. l, taken on the line 'l-"I of this iigure.

Similar parts in these figures are indicated by like reference numerals.

rReferring firstly to Figs. 1 and 7, it will be seen that the cut-out illustrated comprises an insulating tube I, of glass or ceramic material for example, sealed at its lower end into a metallic cup which is formed with a small chamber or space 3, adapted to receive mercury, in communication the bore il of the tube, which in practice is also filled with mercury This bore is shown in i as being slightly enlarged towards end, the central portion of the bore being of uniform diameter.

At the upper end of the tube I is provided a econd metallic cup 5 into which the tube is eil-led in anair--tight manner butin this case the up has a straight open passage I of rlarger di- ,n,eter than, and preferably concentric with, the br oi' the tube forming an overflow or expension chamber for the reception of mercury exy tended from the bore of the tube. In order to September 5, 1930 prevent the extruded mercury from returning to the bore of the tube I by gravity, if the cut-out is to stand in a vertical position, the lower end of the cup 5 isk formed with an upwardly coned base I, the outlet passage 8 from the bore of the tube passing through the apex of this cone.

Suitable contact pins, plugs or the like, such yas shown at 9, are secured in the cups 2 and 5 to project 'laterally therefrom and serve for con-` necting the cut-out into an external electric circuit. v

In order to return the extruded mercury/,from the overflow chamber 6 to the bore 4 there is provided a manually operated piston or plunger IIJ in the overflow chamber with a conical recess II to fit exactly over the upwardly coned base 1 of the chamber so that, when the piston is pressed fully inwards, the void in the overilow chamber is completely filled and the extruded mercury is therefore forced back into the tube.

4Unless the piston I0 were to fit the chamber' with' greater accuracy than is possible under conditions of commercial output a certain'amount of mercury willforce its way between piston and chamber wall when under pressure. An annular groove I2 .is therefore formed in the chamberv wall, ata short distance above the apex outlet ,8. of the cone 'I, which groove is covered bythe piston in its downward movement, to act as a mercury trap from which mercury is returned to the overflow chamber by the rst upward movement of the piston. f

k'lhe plunger or piston I0 may be made of a suitable metal or of a non-metallic substance which is electrically non-conductive, such for example, as the non-conducting materials constituting phenol condensation products and'has an extension or stem I3 which projects through an opening in a removable cap or plug I4 of the enclosing insulating body I5 which is cast around the operative parts of the cut-out.

The capacity of theexpansion chamber 6 and the permitted amount of upward movement of fthepiston I in the'chamber as well'as the crosssectional area of the annular groove I2 forming the mercury trap must be carefully calculated for the varying currents used.

In the construction of cut-outs for the larger currents the upper part of the bore ofthe overflow chamber 5 is flared, as at I6, in order to catch vany surplus mercury which may get above the piston and return it to the lower part of the chamber when the piston is raised. Between the flared top I6 of the chamber and the inner end of the removable-closure cap I4 is aspace I1,

forming an extension of the overflow chamber Q, into which projects a concentric sleeve I8 fixed in the cap ifi. This sleeve is arranged to deiect any mercury which may rise above the flared end E of the chamber 5 and return it to the latter.

It will be seen from Fig. 7 that the moulded casing E5 is formed with heat radiating ribs 55 and with a suitable hand-grip 25.

The bore il oi the tube l and the chamber 3 in the lower cup E may readily be filled with mercury by placing a sufficient quantity thereof in the chamber S oi the upper cup 5, beneath the piston Si?, and alternately raising and depressing the piston or plunger lo, it being found that all the air trapped in these spaces is rapidly displaced by these operations as considerable pressure can be exerted on the mercury.

It may be preferred, however, for purposes of manufacture to connect the upper chamber' 3 to a suitable vacuum pump through a twoway cock, which in the one position opens the chamber to communication with the pump and in the other position opens the chamber to communication with a store or" mercury. As will be Lindestood, the pump is rst allowed to exhaust the air from the interior of the cut-out and the mercury is then allowed to flow in to fill the eyacuated space, by suitable manipulations oi the twoway cock above-mentioned.

The cut-out, when ready for use, contains mercury in the chamber 3, bore and up to the level of the top or the passage 8 in the cone l, a small blob of mercury being left in the annular groove around the latter, it desired, to ensure that the bore 4 will always be completely lled whenever the continuity of the column is re-established by depression of the plunger l0.

The act-ion of the cut-out is as follows:-

Upon a rupture of the mercury column taking place, due to overheating by the passage of a, current in excess of that for which the cut-out is designed, the adjacent ends of the column are forced apart, the upper portion, in part of it, being expelled from the tube l through the passage into the overflow chamber il. The piston Ill is thereby displaced outwardly so uncovering the annular mercury trap l2 and permitting any inercury contained therein to return to the overflow chamber E. The electrical connection between the pins or plugs 9 is thus broken and the external circuit in which the cut-out is incorporated is therefore interrupted.

When it is desired to re-set the cut-out, the piston it is pressed inwards by hand thus displacing the mercury from the overflow chamber into the bore i of the tube and reforming the column.

It will be understood that the metal parts in Contact with the mercury will be made of a metal or alloy which does not amalgamate with mercury, such, for example, as the alloy of aluminum and manganese which is known as duralumin.

A modified construction of the cut-out shown in 2 differs only from that shown in Fig. l in that the tube is shorter and has a uniform bore fi and in that the lower cup il supports by its upper edge a metal member 2a having a downwardly projecting central nipple El) the bore "c of which is in communication with the bore 4 or" the tube i. The other parte co responding to those of Fig. l are similarly designated.

The operation of this form cut-out is almost identical with that ci the to 'm shown in Fig. l, but in this case a slight amount or" air is allowed to remain trapped above the mercury in the cup 2, around the nipple 2b which extends downwardly into the mercury to provide good electrical connection therewith. Upon rupture ci the mercury column the lower portion of the latter is forced downwardly slightly due to the compressibility of the air in the chamber '1, whereby a quick break is ensured, and upon the release of the pressure which occasions such depression of the lower portion or the column, i. e. when the upper portion or the column has been forced out of the bore 4, the compressed air again forces the lower portion of the column part-way up the bore 4. This facilitates the quick re-setting of the cutout.

In Figs. 3 and 4 are shown cut-outs having the piston or plunger disposed laterally of the expension or overilow chamber proper.

Referring to Fig. 3, the general arrangement, comprising the lower cup 2, tube l and upper cup is similar to that of Figs. l and 2 but the upper cup 5 is modied by being closed at its upper end Se and by having the conical base 'i with the central aperture 3 formed as a separate part.

In this case any mercury which is extruded into the upper or overflow chamber G is allowed to flow out therefrom through a lateral downwardly inclined passage 2l communicating with an additional chamber 22 in which is accommodated a plunger 23 of insulating material. The inner end oi the passage 2i opens into an annular groove 2id formed in the wall oi the chamber 6 around the lower end of the cone l.

The additional chamber 22 is formed in the insulating material i5, when this is being moulded around the cut-out parts, by making use oi a suitably shaped core and communicates at its lower end through a tapering passage 2li with a bore 25 extending axially through a nipple 22"; screwed into the wall of the lower cup 2 so that the bore .z

25 opens into the mercury chamber 3 in the said cup.

A correspondingly shaped tapered extension 2l on the lower end oi the plunger 23 is adapted to ll said passage 24 when the plunger 23 is pressed inwardly to the full extent, in which position an annular groove 28 in the plunger registers with the outlet from the passage 2l leading from the chamber 6.

As before, the upper end of the piston or plunger f chamber 22 is closed by a plug I4 through which passes the stem i3 of the Vplunger and in which is secured a central mercury deilecting sleeve i3, the upper portion of the chamber s2 being outwardly ared, as at In operation the plunger 23 is fully depressed and the bore 4 of the tube l is completely filled with mercury. When a rupture of the mercury column occurs tl e upper portion is forced out of the bore 4 and through the aperture 8 into the chamber 5, from which it flows through the pas sage 2l into the groove 23 in the plunge'. At the same time the lower portion of the column is depressed and acts to raise the plunger 23 in the chamber 2".

When it is desired to re-set the cut-out the plunger 23 is raised sudciently to allow the mercury in the groove 28 to now back into the chamber 22, unless the plunger has already been displaced to this extent during the circuit-breaking operation, whereupon the plunger is forced downwardly to press the mercury from the chamber 22, through the passages 24, 25 and chamber' 3, back into the bore of the tube l.

Fig. 4 illustrates a modification of the construe scription.

more, the lateral discharge passage from this chamber is here formed as a tube 29 of insulating material leading into the additional chamber 22 just above the top of the plunger or pistony 23 therein, when this plunger'is in the fully depressed position. f

The upper end of the chamber 22 is flared outwardly at 22a and closed by the plug or cover I4 having secured therein the deflector sleeve I8 and formed with an aperture for the passage of the stem I3 of the plunger 23. The lower end of the chamber 22, however, is formed with an upwardly coned base 3% at the apex of which opens a narrow assage 3l formed in the insulating body I5 and communicating at its lower end with a second rnarrow passage 32, at right-angles thereto, formed partly in the body I5 and partly in the wall of the vcup 2, into the internal chamber 3 of which latter the passage opens.

As described in connection with the plunger i!) of Fig. l, the lower end of the plunger 23 made entirely insulating material is recessed conically at 35i in order to. fit over the baseilrof the chamber 22. f

The operation of the construction just described will be readily understood without further de- Ilteferring now to Figa, it will-be seen that here the general construction of the cut-out is comparable to thatfof Fig. l, the sole essential difference being the replacement of the plunger I0 of Fig. l by a ilexible'diaphragm 34.

A. modification which follows from this is the omission or" Jthe cylindrical expansion chamber 6 of Fig. l and its replacement by an expansion chamber the base of which isformed by a dished metal diaphragm 35 having a central upstanding conical nipple 3S and which is secured to the upper cup 5 by the threaded lower end of said nipple.

An axial aperture 31 formedin the nipple y36v yextends as the continuation passageV 31a in the ycup 5 to the top of the bore 4 in the tube I.

The flexible diaphragm 34 is pressed upwardly at its centre to form a conical depression 38 adapted to t over the nipple 36 and is secured toa push-button 39 of insulating material'which xtends through an aperture in the cap or plug I4 which is screwed into'the insulating body I5 of thek cut-out to hold the diaphragm 34 securely in place.

In'operation, the mercury expelled from the bore 4 of the tube I, upon rupture of the mercury column, is ejected through the passage 31a, 31 into the expansion chamber 6a where it collects around the vnipple Y e To reset the cutout, the push-button 39 is depressed to cause the flexible diaphragm to force the mercury in the chamber 6a back into the bore 4 of the tube i. f f

Fig. 6 illustrates yet another modification which is strictly equivalent `to the form shown in Fig. 1

`wardly and collects around the cone 1.

but differs therefrom in theform of the plunger employed.`

The stem I3 of the plunger is secured in an upper nipplell on a hollow spherical rubber body 4I lhaving a lower nipple 42 forming the plunger proper and moulded with'a recess I I to t over the cone 'I in the base of the upper cup 5.

The plunger 42 and the sphericalbody 4I t closely against the walls of the expansion chamber 6, an annular mercury trap 43 being formed at the junction of the nipple or plunger 42 with the body 4I.

In operation, the mercury expelled from the bore V4 ofthe tube I displaces the plunger up- Upon depressing the plunger by means of the stem I3, in order to re-set the cut-out, the spherical body 4I is flattened somewhat so that its outer wall is forcedv into close contact with the wall of the chamber 6 and prevents any leakage of mercury upwardly past the trap 43. 'The mercury collected around'the cone 'I is therefore returned into the bore l of the tube, I to 17e-establish electrical continuity between the cups 2 and 5 and therefore between the plugs 9 secured therein.

Itv will be noted that in all the forms described the cut-out is renderd as air-tight as is possible in practice so that there is no likelihood of loss of mercury. Attention is particularly called to the fact that in this-structure, the mercury is designed to be used ovrand over again, that is, the initial charge of mercury is used repeatedly, this being possible on account ofthe fact that it is always returned to the bore from the expansion chamber into'which it is thrown on rupture of the circuit due to excessive current. Due to the fact that the cut-.out is made as air-tight as possible, there is no loss or oxidation of the mercury and consequently it hasbeen found possible to use a given volumey thereof indenitely. f

VIt will also be seen that I have provided means for positively forcing back into the tube mercury which has` been expelled therefrom. and that I have provided rneans` for preventing thereturn of said mercuryto the tube until said manually operable means ispositively operated.

l. An electrical cut-out ofthe class 'described including an insulating tube of narrow bore. a mercury column filling said bore. a metallic piece at each end of the tube and in electrical contact with the corresponding end ofthe mercury column, a metallic contact member engaged with each contact piece and serving to connect the mercury column in an electrical circuit to be controlled by the cut-out, a chamber in free' communication with one end of the borecf the tube and .into which mercury is r'expelled from. the tube when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, and a plunger reciprocate-ble within said chamber, sai-d plunger and said chamber being formed to provide an annular mercury receiving sealing recess between the surface of the plungerand the surface of the chamber con# fronting said plunger. ,j

with one end of the bore of the tube and into which mercury is expelled from the tube when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, an extension of said chamber arranged laterally of said insulating tube and communicating with that end of said tube remote from the main expansion chamber, and a plunger reciproca-table within said extension, the wall of said extension and the plunger having one an annular sealing recess and the other extending over said recess and closing it when the plunger is depressed.

3. An electrical cut-out of the character decribed including an insulating tube of narrow bore, a mercury column filling Said bore, a metallic member at each end of the tube in electrical engagement with the corresponding end of the mercury column, means whereby the metallic members may connected in an electrical circuit to be controlled by said cut-out, an expansion chamber in free communication with one end of the bore and having a part thereof extending laterally and below the discharge opening of the bore and into which the mercury is discharged when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, and means independent ef the action of gravity and operative while the cut-out is maintained in its normal position for positively forcing mercury back into the tube.

fl. An electrical cut-out of the character described including an insulating tube of narrow bore, a mercury column filling said bore, a metallic element at each end of the tube in electrical engagement with each end of the mercury column, means whereby the metallic elements may be connected in an electrical circuit to be controlled by said cut-out, an expansion chamber having free communication with one end of said bore, means independent of the action of gravity and operative while the cut-out is maintained in normal position for positively forcing mercury discharged into said expansion chamber by rupture back into the tube, means positively preventing the return of mercury back into the tube until said forcing means is operated, a plunger reciprocatable within said chamber, and means for causing mercury forced upward around the plunger to form a seal across the joint between the plunger and the contacting wall of the chamber.

5. An electrical cut-out as in claim 4 having means for permitting the mercury forming the seal to descend below the plunger when the plunger is raised.

6. An electrical cut-out of the class described, comprising an insulating tube of narrow bore, a mercury column iilling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end of the mercury column, means whereby the metallic pieces may be connected in an electrical circuit to be controlled by said cut-out, an expansion chamber in free communication with one end of the bore of the tube and into which mercury is expelled from the tube when the mercury column is ruptured, an extension chamber arranged laterally of said insulating tube, there being a downwardly extending duct extending from the lower portion of said expansion chamber downward and opening into said extension chamber, the lower end of the extension chamber having an upwardly tapered nipple, the nipple having a bore communicating i maremma with that end of said tube remote from the expansion chamber, the upper end of said extension chamber being enlarged, and a plunger located in said extension chamber and having a recess in its face confronting the nipple and tting the nipple, the plunger being of a length less than the distance between the extreme lower end of the extension chamber and said duct whereby mercury forced up around the piston when the piston is depressed will collect above the piston and seal the joint between the piston and the Wall of said extension chamber, the enlarged upper end of the extension chamber permitting the mercury to flow back into the lower end of the extension chamber when the plunger is fully raised.

7. An electrical cut-out of the class described including an insulating tube of narrow bore, a mercury column filling said bore, a metallic member at each end of the bore in electrical contact with the corresponding end of the mercury column, means for connecting the metallic members in an electrical circuit to be controlled by the cut-out, an expansion chamber in free communication with one end of the bore of the tube and into which mercury is expelled from the tube A:used in said chamber and adapted when depressed to positively force mercury discharged into said chamber back into the tube, and a diaphragm extending between said plunger and the i. all of the expansion chamber, and constituting seal.

An electrical cut-out of the class described, including an insulating tube of narrow bore, a mercury column lling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end of the mercury column, a metallic contact member engaged with each metallic piece and serving to connect the mercury column in an electrical circuit to be controlled by the cut-out, a chamber in free communication with one end of the bore of the tube and into which mercury is expelled from the tube when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, piston means independent of the action of gravity and operative while the cut-out is maintained in its normal position for positively forcing mercury discharged into said chamber by rupture back into the tube, means for positively preventing the return of mercury to the tube until said piston means is operated and means affording a seal around the periphery of the piston when the piston is depressed.

9. An electrical cut-out of the class described, including an insulating tube of narrow bore, a. mercury column filling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end of the mercury column, a metallic contact member engaged with each metallic piece and serving to connect the mercury column in an electrical circuit to be controlled by the cut-out, a chamber in free communication with one endV of the bore of the tube and into which mercury is expelled from the tube when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, piston means independent of the action of gravity and operative while the cut-out is maintained in its normal position for positively forcing mercury discharged into said chamber by rupture back into the tube, means for positively preventing the return of mercury to the tube until said piston means is operated, and means securing a mercury seal between the piston and the Wall of the chamber when the piston is depressed. v

10. An electrical cut-out of the class described, including an insulating tube of narrow bore,Y a mercury column filling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end or" the mercury column, a metallic contact member engaged with each metallic piece and serving to connect the mercury column in an electrical circuit to be controlled by the cut-out, a chamber in free communication f with one end of the bore of the tube and into which mercury is expelled from the tube when vthe mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value,V piston means indeoperated and means for trapping mercury around n the piston when the piston is depressed.

WILLIAM JAMES DAVY. 

